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Multicentre evaluation of Xpert XDR and TrueNat 2nd line tests under field conditions

F Massou(1,2) C Vuchas(6) J C Semuto Ngabonziza(7) S C Agbla(13) O El Tayeb(5) M K Kaswa(9) G Abebe(8) L Camara(11) B Diarra(10) M Camara(12) C Merle(4) B C de Jong(1,3) L Rigouts(1) D Affolabi(2)

1:Institute of Tropical Medicine, Antwerp (Belgium); 2:Supranational Reference Laboratory for Tuberculosis, Cotonou (Benin); 3:Supranational Reference Laboratory for Tuberculosis, Antwerp (Belgium); 4: Special Programme for Research and Training in Tropical Diseases, WHO, Geneva; 5:Damien Foundation; 6:The Bamenda Center for Health Promotion and Research; 7:Rwanda Biomedical Center; 8:Jimma University; 9:Institut National de Recherche Biomedicale; 10:Université des Sciences, des Techniques et des technologies de Bamako; 11:Service de Pneumophtisiologie (Guinée); 12:Université Cheick Anta-Diop de Dakar (Sénégal); 13:London School of Hygien and Tropical Medicine

Appropriate MDR-TB treatment depends on the rapid diagnosis of resistance to fluoroquinolones (FQ) and/or bedaquiline (BDQ). Current tests such as Line Probe Assays do not detect resistance to BDQ or require infrastructures not often available in endemic countries. Recently, two tests have been developed: a new Xpert MTB/XDR cartridge (Cepheid, Sunnyvale) that can detect resistance to Isoniazid (INH), FQ and Ethionamid (ETH) and a TrueNat test (Molbio Diagnostics, Goa) for detection of resistance to INH, FQ and BDQ.

We assessed the performances of these tests in field conditions using phenotypic drug susceptibility testing (pDST) and whole genome sequencing (WGS) as reference standards. Our dataset was composed of 1130 unique samples consecutively collected in the Sub-Saharan African region (Benin, Nigeria, Cameroon, DRC, Rwanda, Ethiopia, Mali, Guinea and Senegal).

Using pDST as reference, performances were:

  •  Xpert XDR : INH ((Sensitivity (Se) : 89.3%, and Specificity (Sp): 95.3), ETH (Se: 28.4, Sp : 93.1) and FQ (Se :72.4, Sp : 99.2).
  • TrueNat : INH (Se : 89.0%, Sp: 83.4) and FQ (Se: 53.8, Sp : 98.3)

Using WGS as reference standard, performances were:

  • Xpert XDR: INH (Se : 84.9%, Sp: 97.2), ETH (Se: 39.6, Sp : 97.3) and FQ (Se :60, Sp : 99.5).
  • TrueNat : INH (Se : 85.6%, Sp: 82.8), FQ (Se: 66.7, Sp : 98.3) and BDQ (Sp : 98.3). No resistance to BDQ was observed.

These tests showed promising results, particularly in excluding resistance to FQ and BDQ.

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